1. Field of the Invention
The present invention relates generally to positioning devices, and more particularly to an ultra-precision positioning assembly.
2. Discussion of Background Art
Positioning devices are widely employed for a variety of tasks in many fields. Depending upon the task, positioning devices typically have tolerances from a few millimeters to a few nanometers. Ultra-precision positioning devices, having tolerances in the nanometer range, are used in applications such as machining (single-point, fixed-abrasive, and loose abrasive), positioning (measurement and inspection devices, optical and laser devices, and astronomy), optics manufacturing and testing (glass, ceramic, and metal), and micro-fabrication (large-scale three-dimensional device) applications.
As tolerances become smaller and the mass of an object to be positioned increases, the positioning device's expense tends to exponentially increase. For example, very large Potassium Di-hydrogen Phosphate (KDP) crystal plates (typically sized as 470 mm×560 mm workpieces ranging in thickness from 10 mm to 100 mm) need to be fabricated for the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. These massive plates must be fabricated on a machine capable of producing a 1.5 micron flat surface, with a depth-of-cut resolution of 50 nm, and able to produce wedge angles in two directions up to plus or minus 0.25 degree. Such a machine would need to possess a difficult-to-achieve combination of long vertical travel, fine positioning resolution, angular tip and tilt capability, and a high degree of mechanical stiffness.
Currently, no such positioning apparatus has been found to exist. Currently available ultra-precision positioning apparatus' are highly complex, costly, and cannot achieve the required performance due to an inability to accommodate the combined requirements for long vertical travel, fine positioning resolution, angular tip and tilt capability, and high mechanical stiffness. In addition, currently available ultra-precision positioning apparatus, when configured for the example use, suffer an additional performance penalty due to overturning moments which tend to distort and disfigure a positioning apparatus during operation. An overturning moment is well known and generally defined as a torque which tends to rotate a body out of a reference plane.
In response to the concerns discussed above, what is needed is an ultra-precision positioning assembly that overcomes the problems of the prior art.